In computer systems firewall protection refers to a security system that monitors all network traffic communications and, based on defined security rules, can block undesirable traffic from entering a system. It represents a barrier between a trusted network and external networks such as those that provide internet access, for example. There are various types of firewalls that fulfil this function.
Inspection state firewalls block access based on the status of a given property, such as a communications protocol or specific port, and make decisions about whether data is transferred to the user based on defined rules.
A proxy firewall acts as an intermediary between the user and the external network and prevents direct contact between them unless incoming data is deemed to be safe although this approach can sometimes degrade performance.
Next generation firewalls combine traditional firewall techniques with network intrusion prevention systems to add an additional layer of analysis to detect threats.